Commit 9474f4e7 authored Jan 16, 2019 by Kees Cook Committed by James Morris Jan 16, 2019

Yama: Check for pid death before checking ancestry



It's possible that a pid has died before we take the rcu lock, in which
case we can't walk the ancestry list as it may be detached. Instead, check
for death first before doing the walk.

Reported-by:  <syzbot+a9ac39bf55329e206219@syzkaller.appspotmail.com>
Fixes: 2d514487 ("security: Yama LSM")
Cc: stable@vger.kernel.org
Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: James Morris <james.morris@microsoft.com>

parent a811dc61

security/yama/yama_lsm.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -368,7 +368,9 @@ static int yama_ptrace_access_check(struct task_struct *child,
		break;
		case YAMA_SCOPE_RELATIONAL:
		rcu_read_lock();
		if (!task_is_descendant(current, child) &&
		if (!pid_alive(child))
		rc = -EPERM;
		if (!rc && !task_is_descendant(current, child) &&
		!ptracer_exception_found(current, child) &&
		!ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE))
		rc = -EPERM;

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